Carbon nanotube (CNT) electrodes for electrochemistry were fabricated from single- and double-walled carbon nanotubes. The electrodes were subsequently covalently loaded with a ferrocene modified a-aminoisobutyric acid peptide, and the electron transfer (ET) capabilities were probed with cyclic voltammetry. The CNT electrodes comprised of double walled CNTs (DWCNTs) demonstrated significantly higher peak current compared to their single walled counterparts (SWCNTs). This is attributed to a higher loading of the ferrocene modified peptide to the outer wall of the nanotube, through the presence of a larger number of defects sites within the sp(2) carbon lattice for the DWCNTs. This higher loading was achieved without compromising the ET rate, indicating that DWCNTs may offer a useful alternative to SWCNTs in future electrochemical sensors and biosensors. (C) 2012 Elsevier Ltd. All rights reserved.